1. Field of the Invention
The present invention relates to a delivery server and a content delivery method in the delivery server as well as a multicast server and a content delivery method in the multicast server, and particularly relates to a delivery server and the like delivering contents such as video and music to client terminals through a network.
2. Description of the Related Art
In recent years, a movement toward construction of a Next Generation Network (NGN) which replaces a telephone network in a circuit switching system of related art with a network constructed based on an IP (Internet Protocol) technology becomes active. The NGN has a band guarantee function and a security function in the network itself, in which session control is performed by using a Session Initiation Protocol (SIP).
In the above NGN, a client terminal is capable of receiving delivery of contents such as video and music from a delivery server. In this case, it is extremely difficult to know how much there are delivery requests from client terminals to the delivery server and to identify server resources necessary at that time.
Systems in which contents such as video and music from the delivery server (a content providing server) to client terminals (user terminals) are delivered through a network such as Internet are described in, for example, JP-A-2004-110277 (Patent Document 1), JP-A-2005-327155 (Patent Document 2) and JP-A-2004-7228 (Patent Document 3).
FIG. 14 shows a state in which streaming delivery of taken image data is performed from a camera server 210 as the delivery server to client terminals 220a to 220c through a network 230. The number of streaming deliveries which can be performed by one camera server 210 is limited due to the CPU (Central Processing Unit) power and so on. In this case, when streaming delivery with high image quality is performed, the number of deliveries is further limited.
Accordingly, load balancing systems have been proposed in order to increase the number of deliveries in related art. As the load balancing system, there exists load balancing by a DNS (Domain Name System) as shown in FIG. 15. In the load balancing system, when there is an inquiry about an IP address of the delivery server from a client terminal 220 to a DNS server 240, the DNS server 240 notifies the client terminal 220 of IP addresses of a delivery server (server 0) 210a to a delivery server (server 2) 210c by sequentially allocating IP addresses of these servers, as a result, loads of respective servers are balanced.
Also as the load balancing system, there exists load balancing by a load balancer (switch) as shown in FIG. 16. In the load balancing system, when there is an inquiry about the IP address of the delivery server from the client terminal 220 to the DNS server 240, the DNS server 240 notifies an IP address of a load balancer 250, and the load balancer 250 sequentially allocates the delivery server (server 0) 210a to the delivery server (server 2) 210c, as a result, loads of respective servers are balanced.
Additionally, multicast systems are proposed in order to increase the number of deliveries in related art. As the multicasting systems, an IP multicasting, an application-level multicasting and the like are known.